Preservation of color in green vegetables



United States Patent PRESERVATION OF COLOR IN GREEN VEGETABLES NoDrawing. Application May 18, 1955 Serial No. 509,405

5 Claims. (Cl. 99 -186) This invention relates to improvements inpreservation of color in green vegetables and has for its object toprovide a method whereby the composition of the can contents will bemaintained at the same pH level for prolonged periods notwithstandingthe change which takes 'place in the canned vegetables during storage.It is well known that the change in color of green vegetables during thecanning process is due to the breakdown of the chlorophyll. It is alsoknown that such color change can be largely prevented by employing analkaline canning solution such that the alkalinity of the canningsolution at the conclusion of the canning process is approximately8.0-8.5 pH. Considerable effort has been directed'toward the developmentof canning solutions having an alkalinity of this order which will notadversely affect the taste or texture of the canned product.

It has been noted, however, that vegetables so processed will still havetheir natural green color it consumed within a short period aftercanning, while identically prepared cans, if maintained in storage for aperiod of months, will develop the greenish yellow appearance ofvegetables canned in the usual sugar-salt canning solution which issubstantially neutral at the conclusion of the canning process. Thischange in color is due to a progressive change in alkalinity duringstorage for I have noted that a canning solution which had a pH of8.0-8.5 at the conclusion of the canning process will, after eight orten months storage at ordinary warehouse temperatures, have a pH in theorder of 7.0-7.5, with changes of lesser magnitude after shorter periodsof storage under like conditions.

I have discovered that the alkalinity of the canning solution may bemaintained within the range required to preserve the green color byproviding the can with a lining of suitable material having alkalinecompounds incorporated therein in such manner that the compounds willleach out of the lining slowly over a period of months.

The following are specific examples of preferred procedures for carryingout my invention.

Example I with the above solution to such extent as necessary tobulld upa film of 1-2 mils thickness when the solvent has evaporated. In lieu ofthe ethyl acetate a mixture of 80% toluene and ethanol may be used asthe solvent. The film formed as above, described on the inner surface ofthe can, is sufficiently hydrophilic to slowly absorb the aqueouscanning solution, which grad ually leaches out the alkali, therebyretarding the change in pH which would otherwise take place.

A suitable grade 3 as Elvanol, a Du Pout product, and 1% of a watersoluble In lieu of the magnesium hydroxide, other suitable alkalinecompounds may be used, for example, disodium glutamate, which ispreferably employed alone or in conjunction with magnesium hydroxide togive the de-' sired alkalinity to the canning solution during thecanning process. The disodium glutamate may be substituted in whole orin part for the magnesium hydroxide in the coating applied to the wallsof the can. Other compounds may be substituted for disodium glutamate asbuffers, particularly the sodium salts of certain amino acids and otherorganic acids, for example, glycene, asparti acid, tyrosene, citric acidand thytic acid are most effective as bufiers in the pH range which itis desired to maintain.

Example. I]

amount of a water soluble alkali of the character mentioned above, 4% byweight of a synthetic resin known alkali catalyzed heat reactivephenolic resin. The interior of the can is coated with the abovesolution and is baked 30 minutes at 325 F. The coating when dried,should be in the order of 1-l.5 mils in thickness.

Example III A resin solution is prepared by adding to a solventconsisting of xylene 84.5%, butanol 8.7%, and naphtha 6.8%, a mixture ofsynthetic resins consisting of 7 parts of an epoxy resin and 3 parts ofa melamineformaldehyde resin. The ratio of resin to solvent shouldsoultions and is hence rendered more absorptive as the alkalinity of thecanning solution tends to decrease. The

particular resins may be Epox 1007 from the Shell Chem-- ical Companyand Melamax 2458 of the American Cyanamid Company. Before applying thecoating to the can Mg(OH) is added in an may be substituted for theMg(OH) Example IV Instead of a resin or plastic coating, as specifiedabove, a suitable coating may be prepared from soy bean oil which isentirely innocuous as an additive to the canned product. Soy bean oil isair blown at C. to a viscosity of E measured on a Gardner-Holdt tube,and a? peroxide value of 334. The soy bean oil is renderedalkali-resistant by styrenation. This is accomplished by' adding to 58parts of the blown soy bean oil, 29.4 parts of styrene'and 12.6 parts ofmethyl styrene.

lowed to stand for 8 hours. There is then added to 325 parts of thestyrenated blown soy bean oil 57.6 parts- This is heated at 230- Thereis then added phthalic of glycerol and one part lime. C. for about onehour. anhydride parts and xylene 20 parts. This is then heated for about3% hours at 230 C. and thinned with xylene to the desired viscosity forapplication to the cans after the addition. of the necessary amount ofthe alkaline salt, to leave in the film formed on the evaporation of thesolvent a quantity of compound in the same The baking order as obtainedin the foregoing examples. schedule is preferably 45 minutes at 300 C.

The amount of solvent added is, of course, not critical 1 and dependsupon the method used for coating cans.

Patented Feb. 24,1959

It is also alkali-resistant, thatamount approximatelythe same by weightas the added resin. Any alkaline compound suitable for addition to thecanning solution The mix- 1 ture is heated at 122 C. for a two-hourperiod and al-j If thelayersare"built upby-Irepeated spraying andalternate dry g. aigrcaten amount. of. solvent, will be vused.

than when the coating is applied in one operation.

Example. V Analkali-resistant pheliQlie resin ,isproduced by adding to100 pounds ;:Bakelite;,l2.5" gallons tung oi1.. The ,mix-

ture is heated (l-E4 50? ion--30 minutes and isthen thinned bytheadditionof ,Z'ZVzgallons of xylol. To this is added 100. pounds. of a 1mixture of; alkaline compounds, for example,- magnesium hydroxide 70pounds magnesium ascorbate'30 pounds. Xylolis then added to give, the

desired; fluidity for the; coatingoperation. Baking schedulez 30 minutesat 325'. F.-

tihenolf tormmdehyfde restrict thethefmosetting type; and 30%'-50% ofmagnesium hydroxide: are-mixedrinit.

The surface of the can is then enameled with this foamresinand thenbaked, preferably for 30 minutes at 325 An equivalentamount,ofaisuitable alkali compound suchas hereinafter mentioned maybeused and the foam;

resincoating-maybe applied over a lining of impervious; resin ifdesiredto prevent contact of the contents'of the,

metalof the can; The foam resin on setting is microporous andthealkaline compound will slowly, leach O'IJtIQf the pores of theresin'and maintain thepHof the canning-solution within'the desired rangeThe porosity of the foam-resin maybe'modified by adding with themagnesium hydroxide or other alkaline compound a water soluble substancewhich is innocuous in the canning solution,- for;examp1e, lactose; Thistype oflining depends for" its leaching-qualities on the passage= ofthe; canning solution in contact with the, surface to andthroughsuccessivepores-as the storage period continues: By theadmixture of-thelactose the surface meant the pores for absorption: ofthe liquid isprogressively, increasedias-thelactoseis dissolved out of'theresin.Instead of usin a waterimpervious material for 'the .foamresin aslightly hydrophiliclresin such as above described maybe advantageouslyused;

A microporouseresin may also be prepared-by adding finely ground porousmaterial such as silica gel, diatomaceous 1 earth and thelike to theresin along with; the selected;alkalinegcompound.

In the foregoing examplesIhave referred to mag. neslum. hydroxide; as:a; suitable alkaline compound.- Other-.2 alkaline compoundsmayxofcoursebe used, for

contents. The coatings;heretofore applied are effective for: theirintended purposeto the extent that they'are completely non-reactive andprovide. a continuous adherentprotectivecoating for the'entire surfaceof the metal. My improved can liningmay' be applied to cans having sueh:linings;- Where the commodity packaged.- is adverseiaffected; by,contact with the metal.

It -is;,not :necessary that-:my improved can lining coverthfieentirea-surfaceof:the can, but on :the contrary, more uniformresults will be-.obtained*if the'lining is confined t0.-the:.wal1-of-thecan as distinguished'from the ends. Therquantity ofalkalileached out of the lining is dependent on the area of the lining thatis" in contact withftheeliquid contents; of the can. stored withthe-cases inwhich they-are packed positioned soythat thecans arevertical, one end or the other ofthe andapparatusmow in use for coatingthe inner.

If i the cans are can will be out of contact with the canning solution;whereasqifthecases arepositioned so that the cans are resting on theirsides the surface of the can which 15 not wetted by the canning solutionwill be greatly reduced.

If, however, the alkalized lining is applied only to the surface of thewalls of the cans as distinguished from the ends, the wetted surfacewill"be-approximately the same regardless of the position in which. the-cans.:a,re--stored. Also, of course, the lining need not cover theentire surface of the Walls of the can, but may be applied in stripes orotherwise inlimited areas to thereby reduce the surface of'th'ealkalized'resin which is wetted'by the canning solution. That is to say,the same quantity of alkalized resin canpbe, applied-Vto;thicke-fi1ms;to limited areas of the exposed surface-of :the cans andthus. reduce the rate at which; the alkali v willbeleached out of theapplied coating.

Instead of confining the alkalized coatings to a limited area-rot; the:canning; surface the leachi g: f; th alkali fromflhjer coating may; beprolonged y pP1yi,11e he; alkalized coating, to; the can and-thereafter;applying-az very thin coatingofanon absorptivei non-hydrophilic' resin,such tasgnowemployed for Protective coatings, over the hydrophiliccoating. Thepfilm of non hydrophilic coating ;can be readily applied -byspraying.;orotherwise-- in layersthin-enough to have alimited.-porosity, thereby reducing. to any desired extent the.- rate ofabsorption of i the hydrophilioundercoating. y 7,

Instead o-fincorporating the: alkaline: compoundsrin the coatingmaterial the resinous,coating rnayvbe, applied-to; the can;,wallsandiwhile-still ;viscousihe alkalinecomv pounds may,;be-; dusted onthee-coating; or; otherwise -,embedded in the surface-30f;theicoating.,A; thin oyerlay er, of a non-hydrophilic .material may; then; beqappliedto: reduce the rate atwhich thealkali will.be,-dissolved; in the canningsolution.

It will be understood, that my invention is not limited to anyparticular; alkaline compounds or combinationgofi compounds or to anyparticular resins or othercoating materialr It'is essential thatthe.selectedmlkalinecom pQun-dsand resinstbeinnocuousand ohm-characternot, to adversely, affect the taste or: texture] of, the can vegetablestIt is: also essential, that; thQnIGSiIlg: hoof; as charactensuch thatthealkali ;wil l slowly-:dissolve out Off; the coating:in;order ;to pro1ongthe; storage perioiduring; which; thealkalinity. oi the. canningsolutionwill llearnairjnv tained: aboveithesdesired minimumwitheutzatanyime; producing .1 azdegree: of alkali-nay whichzwo ldabeeunsuitr ablefrom the standpoint oftasteandtenturet;

It .will be; anderstoddiv the-rgnfore,-.v thatgmy: invention is notlimited: to: the: specific compositions mentioned? but thati the; samemay be;v variously-, modified within the? scopegof-zthe appended claims.

In; thez foregoing: specification and. i claims the;- expresv sionalkaline compound? is:;used generically: toqinclude compounds which whenadded to the aqueous solutionl such:aszthe-iconventional:canniriglsolution, willwtend to: increase the pH of theEsolution'i Iclaim:

1. A canned food product'consisting of a hermetically sealed metalcancontaininga green vegetablein an alkaline canning solution, theinterior of the surface-of the can having acoating consisting? of-{acomposition. containing an innocuous alkaline compound-1 which issoluble in the canning solution,- saidcoating-andcempound b'eingof-such-character that the aisaline compound will progressively dissolvein the"canninga'solutidn' overza prolonged pcriodof-time wherebythe-pH"offthe canniiig solution" is maintained sub'stantiz'tllyunchanged for the" prolonged =period of time.

2. The canned dood'product' ofclaim .l' wherein the coatingcompositionis slightly hydrophil'i'c.

3; The canned, food product of claim,2 wh'e'rein theh'ydr'ophiliccoating composition is coverediwith a thin, film ofnon-hydrophilic composition.

Jim

4. The method of preserving color in canned green vegetables whichconsists in placing the vegetables in an alkaline canning solution andadding to a portion of the interior surface of the can a coatingconsisting in part of an innocuous alkaline compound which is soluble inthe canning solution, said coating and compound being of such characterthat the alkaline compound will progressively dissolve in the canningsolution over a prolonged period of time to maintain the pH of thesolution at a substantially unchanged value for the prolonged period oftime.

5. The process of claim 4 wherein the coating composition is slightlyhydrophilic.

Baekeland May 3, 1910 6 1,966,856 Grofi July 17, 1934 2,047,957 FletcherJuly 21, 1936 2,067,134 Zabel Jan. 5, 1937 2,133,117 Schroder Oct. 11,1938 2,189,774 Blair Feb. 13, 1940 2,318,426 Schroder May 4, 19432,336,785 Guernsey Dec. 14, 1943 2,473,747 Giesker June 21, 19492,589,037 Bendix Mar. 11, 1952 FOREIGN PATENTS 402,877 Great BritainDec. 14, 1933 OTHER REFERENCES Industrial and Engineering Chemistry,October 1954, pages 2226-2232.

4. THE METHOD OF PRESERVING COLOR IN CANNED GREEN VEGETABLES WHICHCONSISTS IN PLACING THE VEGETABLES IN AN ALKALINE CANNING SOLUTION ANDADDING TO A PORTION OF THE INTERIOR SURFACE OF THE CAN A COATINGCONSISTING IN PART OF AN INNOCUOUS ALKALINE COMPOUND WHICH IS SOLUBLE INTHE CANNING SOLUTION, SAID COATING AND COMPOUND BEING OF SUCH CHARATERTHAT THE ALKALINE COMPOUND WILL PROGRESSIVELY DISSOLVE IN THE CANNINGSOLUTION OVER A PROLONGED PERIOD OF TIME TO MAINTAIN THE PH OF THESOLUTION AT A SUBSTANTIALLY UNCHANGED VALUE FOR THE PROLONGED PERIOD OFTIME.